Fireproofing cellulose with complexes of heavy metal salts of acid phosphate esters

ABSTRACT

COMPOSITIONS WHICH ARE WATER-SOLUBLE AMMONIA COMPLEXES OF HEAVY METAL SALTS OF ACID PHOSPHATE ORGANIC ESTERS, THE ORGANIC GROUPS CONTAINING AN AVERAGE OF AT LEAST THREE CARBON ATOMS, ARE USED IN WATER SOLUTIONS TO PRODUCE WEATHER-RESISTANT FLAME-RETARDING TREATMENTS FOR WOOD AND OTHER CELLULOSIC BODIES. THE ORGANIC MOIETIES ARE PREFERABLY CHLORINATED OR BROMINATED TO IMPROVE THEIR FLAME RETRADANCE.

'United States Patent: Oifice 3,740,264 Patented June 19;, 1973FIREPROOFING CELLULOSE WITH COMPLEXES OF HEAVY METAL SALTS OF ACIDPHOSPHATE ESTERS Charles Andrew Lynch, Jr., Severna Park, and EdwardFrancis Orwell, Baltimore, Md., assignors to FMC Corporation, New York,NY.

No Drawing. Original application Mar. 27, 1970, Ser. No. 23,479. Dividedand this application Dec. 15, 1971, Ser. No. 208,504

Int. Cl. C09k 3/28 US. Cl. 117-136 5 Claims ABSTRACT OF THE DISCLOSURECompositions which are water-soluble ammonia complexes of heavy metalsalts of acid phosphate organic esters, the organic groups containing anaverage of at least three carbon atoms, are used in water solutions toproduce weather-resistant flame-retarding treatments for wood and othercellulosic bodies. The organic moieties are preferably chlorinated orbrominated to improve their flame retardance.

BACKGROUND OF THE INVENTION This is a division, of application Ser. No.23,479, filed Mar. 27, 1970 now Pat. No. 3,678,086.

The problem of producing cellulose structures which are nit readilycombustible has been the subject of much study for many years. Theproblem is how to get a fireretardant material into the cellulose, at asufliciently low price to warrant the advantage gained, withoutsacrifice of the desired properties of the cellulose structure, such asstrength and appearance. In addition, where the cellulose is exposed tothe weather, as with wood in structural applications and cotton clothwhen used for tents and tarpaulins, the flame-retarding agent mustsurvive the hazards of weathering.

Both the phosphate radical, and the halogens chlorine and bromine, havewell-known utility in flame-retarding compositions, having beenextensively used for that purpose, separately and in combination. Inaddition, the utility of heavy metal salts of phosphoric acid is wellknown. The problem has always been to combine these, and other materialswith fire-retarding properties, into combinations which meet therequirements of low cost-including both original cost and that ofapplicationwith utility for the desired end result.

Organic esters of phosphoric acid-e.g. tricresyl phosphate-are known toimpart flame-retarding properties to compositions in which they areincluded, and more so when the organic moieties are halogenated withchlorine or bromine. And metal and other salts of monoand/or diacidphosphate esters have been used for their combination of flameretardance and plasticizing propertiessee Tattersall U.S.Pat. 2,202,124,who used such salts of dimethyl phosphoric acid as a combined flameretarder and plasticizer for nitrocellulose, or Harrington, J r. et al.US. Pat. 2,933,402, who used heavy metal salts of bisUi-chloroethyl)phosphoric acid for similar purposes in cellulose acetate filaments.Similar salts have also been used in lubricantssee for example Asseff etal. US. Pat. 2,916,906 and Bonmartini et al. US. Pat. 3,000,821.

While the literature teaches that the metal salts of acid phosphateesters would impart filame retardance to cellulose structures, attemptsto use them have given poor results. The cost of application in organicsolvents, and the general poor weather resistance of the salts suggestedby Tattersall and Harrington, Ir., have discouraged furtherexperimentation.

SUMMARY OF THE INVENTION We have discovered that heavy metal salts ofacid phosphate esters can be used economically ot give weatherresistantfire retardance to cellulose structures such as wood and cotton cloth,by making new compositions which are ammonia complexes of heavy metalsalts of acid phosphate esters in which 1 to 2 hydrogens are availablefor each phosphorus to form salts, and the organic ester groups have anaverage of at least 3 carbon atoms per ester group where a halogen ispresent and 4 where there is no halogen. The upper limit for carbonatoms in the ester groups depends on the nature of the ester groups, andthe degree and type of halogenation. For alkyl groups, the upper limitcan be expressed as C atoms-Cl atoms2(Br) atoms==6 for aryl groups,

C atoms-Cl atoms-2(Br) atoms=10 The complexes are dissolved in water,and the solutions are used to impregnate cellulose structures. Thestructures are then dried at temperatures high enough to drive off theammonia; air drying is sufiicient, but low heats are preferred to hastenprocessing.

DESCRIPTION OF THE INVENTION AND THE PREFERRED EMBODIMENTS In practicingthe instant invention, the starting material is an acid phosphate ester,in which 1 to 2 of the 3 active hydrogens of phosphoric acid arereplaced by the residue of an alcolol or phenol. The choice of organicradicals of the esterifying hydroxy compound is limited by the necessitythat the final composition be both resistant to leaching by water, andact as a flame retardant.

Unsubstituted or alkoxy-substituted alkyl radicals used in the estershould average at least 4 carbon atoms to ensure proper resistance toweathering, and cannot average more than 6 carbons; above this figure,fire retardance imparted by the metal phosphate portion of thecomposition is otfset by the carbon-hydrogen content of the alkylgroups. However, if the alkyl groups are halo-substituted by chlorine orbromine, 3 carbon atoms is the lower limit, and more carbon can betolerated at the upper limit. A formula which can be used forcalculating the permitted maximum carbon in alkyl ester groups is CatomsCl atoms-2(Br) atoms='6 With aryl compounds, the formula isapproximately C atomsCl atoms-2(Br) atoms=l0 The acid phosphate esterscan be prepared by a variety of known methods. These include (1)hydrolysis of complete phosphate esters, or of alkyl or arylphosphorochloridates; (2) dehydration of mixtures of alcohols andphosphoric acid to produce monoesters; (3) reaction of polyphosphoricacid with an alcohol or a phenol to produce chiefly monoester; and (4)reaction of an alcohol or phenol with P 0 to produce a roughly equimolarmixture of monoand diester. We prefer this last method, since it is byfar the most economical.

Halogenated esters can be prepared from halogenated alcohols or phenols,or the acid ester can be halogenated.

The partial esters are then reacted with a heavy metal compound whichwill form a complex with ammonia. A great many metals will do so, butwhile they are theoretically useful, they are not economically useful oncost considerationse.g. cobalt, nickel, tellurium, ruthenium, silver,cadmium, rhenium, osmium, iridium, palladium, gold, and mercury(although a very minor amount of mercury is useful if Wood is to beprotected against fungi as well as against flame). Economically soundmetals include iron, chromium, manganese, copper, zirconium, and zinc.The last two give treatments with minimum color, and are consequentlypreferred, with zinc being the metal of choice on economic grounds.Copper, being an effective anti-fungal agent, is a metal of choice,despite its color, because of this dual role.

The salts may be conveniently prepared by reacting the acid esters withmetal oxides, hydroxides, sulfides, or carbonates of the metal, or bydouble decomposition of salts-e.g.

After salt formation, complexing is done by adding suflicient ammonia toform the water-soluble complex.

Impregnation of articles to be treated can be done in a variety of ways,and there are many variables. Some of these variables are:

(1) Concentrations and amounts.The amount of salt to be deposited withinthe treated article based on dry weight of the article is highlyvariable. In the case of fire retardants, the amount is fixed oneconomic grounds which is variable depending upon service required.Articles having a relatively high surface/volume ratio will requirehigher rates of application than massive articles. Impregnations to gainpreservative properties may require a smaller concentration of salt thanfor flame retardant properties.

Having fixed the amount of salt desired per unit weight of the articleto be treated, the concentration in the impregnating solution will varywith the absorptivity of the article, depth of treatment desired, andapplication method. Thus, pressure or vacuum impregnation may require alesser concentration than dipping, in turn less than surface spraying.

In vacuum treatment of shingle strips, absorptivity varied from 50 to150 percent of the shingle weight. Impregnating solution concentrationsvaried from 15.5 to 2 percent. Impregnation levels of dry salt in dryshingle varied from 1 to 20 percent.

(2) Temperature.lmpregnation has been accomplished primarily at roomtemperature. Warmer temperatures will increase solubility of the salt,and accelerate the impregnation process. Temperature during impregnatingand drying, however, should not exceed 70 C., above which strength andproperties of the treated article may be affected.

(3) Pressure.Application of vacuum and pressure may be applied to aidimpregnation. Similarly, the treated article maybe vacuum dried toremove water and released ammonia.

(4) Time.There are no process reasons for strictly specifying time,other than reasons of economic productivity.

(5) Equipment.Dipping vessels, pressure impregnating vessels, and driersare used for impregnations in industry. Design details of processingequipment are not a part of this invention.

Once the desired impregnation has been accomplished, water is removedfrom the impregnated articles by air drying, as by blowing currents ofair, by heat, or by combination of air currents and heat.

It is important that the water and complexing agent be removed, or thetreatment will not withstand weathering.

We have impregnated various wooden articles such as shingles, siding,two-by-fours, and other structural elements, as well as tenting canvasand other textiles, with varying concentrations of complex. Obviously,flame retardance is improved with increasing levels of additives, allthings being equal,

Both chlorine substitution, and particularly bromine substitution in theesters, contribute markedly to improvement of flame retardance; wherelow levels of pickup are desired for mechanical reasons, best resultsare obtained with halogenated esters. The utility of these halogens forthis purpose is of course well known.

EXAMPLES The following examples of the invention are given by way ofillustration and not by way of limitation:

EXAMPLE 1 A 3-liter flask was equipped with a pot thermometer,condenser, stirrer, and P 0 adding device comprising a l-literErlenmeyer flask connected to the flask side-arm by means of wide boretubing with a clamp to regulate the P 0 addition rate. n-Butanol (777grams, 10.5 moles) was charged into the flask, which was purged withnitrogen and cooled in an ice bath. The P 0 (497 grams, 3.5 moles) wasadded in 105 minutes at 35-50 C. The mixture was heated to 70, held at70 for 15 minutes, then allowed to cool to room temperature. The productwas a slightly amber slightly turbid solution. Its equivalent weight tothe phenolphthalein endpoint was 143.

One equivalent (143 grams) of mono/dibutyl phosphoric acid was dissolvedin 369 grams water and 59 grams (1.0 mole) of concentrated NH OH toproduce 571 grams of ammonium salt solution. Cupric sulfate solution(400 grams of 20 percent solution, 0.5 mole) was added in 40 minutes at2831 C. to produce a pale blue slurry of the cupric salt. Two moles ofconcentrated NH OH (117 grams) was added but failed to dissolve theprecipitate completely. Of the 1088 grams of slurry, 84 grams wasremoved for solubilization experiments. The addition of 28 grams ofconcentrated NH OH to the balance of the slurry completed solubilizationand produced 1032 grams of a dark blue solution. The solution contained2.17 percent phosphorus, 2.84 percent copper, 3.85 percent ammonia, and5.9 percent ammonium sulfate. Since the equivalent weight of thecomponent acid mixture was 143, the average molecular weight of thecupric mono/ dibutyl phosphate (ammonia-free) is 347.5. The cupric saltconcentration, expressed on that basis, was 15.5 percent.

Cedar shingles were cut from the butt end into strips 5 inches by /2inch. The strips were only air-dry before impregnation. Tests showedapproximately 7 percent moisture removable at 50/25 mm.

Impregnation with the copper salt solution was accomplished by immersingthe solution, evacuating to 25 mm. and releasing the vacuum. The cyclewas repeated five times. Four such strip impregnations were made withfull-strength solution, and further i'mpregnations were made usingsolution diluted to 50 and 25 percent strengths. The strips variedwidely in absorptivities, varying from 50 to percent weight pickup.Impregnation levels were calculated as:

Wet pickup weight X solution strength original strip weight In this way,a graded series of impregnation levels, varying from 1.9 to 13.1 percentas cuupric mono-dibutyl phosphate (av. MW 347.5), was provided. The wetstrips were then dried to constant weight at 4550 C./ 25 mm. Complexedammonia was released, depositing the less soluble copper salts withinthe structure of the wood.

The burning tests were conducted according to ASTM D635. In brief, thistest consists of marking the specimen one inch and four inches from theend, supporting the specimen in a horizontal position with itstransverse axis inclined at an angle of 45 and igniting the end with aburner. If the specimen burns to the four-inch mark, it is judgedburning by this test and a burning rate calculated. If the specimenburns past the o11e-inch mark but does not reach the four-inch mark, itis judged selfextinguishing by this test. If the specimen does not burnpast the one-inch mark, it is judged non-burning by this test. Threeburning samples in a set of ten, regardless of the performance of theother seven, dictate a rating of burning for the material.

In the case of the untreated specimens, three of six burned at anaverage rate of 2.77 inches/minute. All of the treated specimens werenon-burning.

TABLE I.BURNING TESTS ON CEDAR SHINGLES IM- ggfigglATED WITH CUPRIOMONO/DIBUTYL PHOS- A. Non treeted Burning time, Burned length,

specimen seconds inches Rating (a) 63 3 Burning.

(b) 85 S.E.

(c) 33 S.E.

(d) 72 3 Burning.

(e) 60 S.E.

(f) 61 3 Burning.

Burning B. Treated Percent time, Burned specimen Cu salt seconds lengthRating D510-141-21 1. 93 27 Non-burning.

D5l014037 3. 63 15 0 Do.

D5l0-14CH14 4. 70 12 0 D0.

D510l3731 7. 90 15 0 Do.

D5l0-l37-39. 8. 35 13 0 D0.

D51010423 13. 5 0 0 Do.

1 Burning time reported for non-burning samples is the time the specimenflamed after the flame source was removed.

NOTE.AVerage burning rate 2.77 in./min.

Example 2 One equivalent of the ammonium mono/dibutyl phosphate solutionof Example 1 was precipitated by the addition of 400 grams of 25 percentaqueous zinc sulfate. The white precipitate was dissolved by theaddition of ammonium hydroxide and impregnation and drying was conductedas before to produce a series of strips containing from 3.3 to 11.8percent of the zinc salt. All strips were non-burning, with theexception of the strip at the lowest impregnation level. This strip wasrated selfextinguishing.

Example 3 Copper and zinc salt impregnations of cedar shingles wereconducted as previously desecribed. Twelve strips impregnated with thezinc salt in the range of 1.4 to 7.25 percent by weight were prepared,along with 15 strips impregnated with the copper salt at impregnationlevels varying from 2.5 to 12.1 percent. Each of these strips weresubjected to a severe accelerated weathering exposure comprising cycleseach consisting of immersion in water at 140 F. for 8 hours, followed byoven-drying at 140 F. for 16 hours. Each strip was then subjected to theburning test, ASTM D635. Of the 12 strips treated with zinc salt, 10were self-extinguishing, and 2 were burning. The impregnation levels ofthe 2 burning samples were 1.5 and 1.6 percent. All of the stripstreated with copper salt were self-extinguishing.

Example 4 The procedure and apparatus described for the butyl derivativewas utilized for this preparation. Propylene chlorohydrin (850.5 grams,9 moles) was charged to the flask and 426 grams (3 moles) of P 0 wasadded at 5060" in 4 hours. The mixture was held at 50 C. overnight. Theequivalent weight to the phenolphthalein endpoint was 160.1. The productwas soluble in an equal weight of water.

The free acid (160 grams, 1.0 equiv.) was dissolved in 400 ml. of waterand treated with 59 grams (1.0 mole) of concentrated NH OH (29% NH togive a solution having a pH of 5. To the solution was added 323 grams(0.5 mole) of 25 percent ZnSO solution to form a light tan slurry of thezinc salt. The salt was solubilized by the addition of 168 grams ofconcentrated NH OH. The turbid solution was filtered to remove suspendedsolids, then diluted to form a 10 percent solution of zinc mono/di(chloropropyl) phosphate (av. MW, 383.4). One portion of the solutionwas diluted to a 5 percent concentration and one portion to a 2.5percent concentration. The solutions were used to impregnate cedarstrips. Eighteen strips, varying in add-on from 1.3 to 21.0 percent wereprepared and subjected to the weathering test of Example 3. All of thestrips were self-extinguishing.

Example 5 Example 4 was repeated, using zinc bis(2,3-dibromopropyl)phosphate as the metallic-organic phosphate. All strips produced wererated non-burning in the test.

Example 6 Mixed mono/di-butyl phosphoric acid, prepared as in Example 1(486 grams), was treated with 284 grams of gaseous chlorine at 30-50 C.under ultraviolet activation. The weight increase was grams and theequivalent weight of the product was 143 after dissolved gases werestripped under vacuum. After washing with an equal weight of water, anddrying, the equivalent weight was 154.

One gram equivalent of this acid (154 grams) was dissolved in 400 gramsof water and 59 grams of 29 percent NH OH. The solution was furtherdiluted to 1856 grams with water to produce a 10 percent solution of themixed zinc salt.

Cedar shingles were impregnated with ammoniacal solutions as describedpreviously to provide a series of strips varying in dry add-on from 3 to12 percent by weight. After subjection to the severe weatheringconditions of Example 3, the standard burning test resulted in a ratingof self-extinguishing for all samples. Maximum burning length was oneinch.

Example 7 Mixed mono-diphenyl phosphoric acid was prepared by treating988 grams of molten phenol gradually with 497 grams of P 0 under N at5055 C. Heating was continued until the P 0 was substantially dissolved.The product (Neutral equiv. 184.5) gradually crystallized in storage.

The product was dissolved in ammonium hydroxide solution, precipitatedwith ZnSO and redissolved with ammonia as usual.

Impregnation and Weathering was carried out as before. Of 11 stripsvarying in add-on from 3 to 13 percent, all were ratedself-extinguishing. The maximum burnlength was 1.25 inches.

Obviously, the examples can be multiplied indefinitely, withoutdeparting from the scope of the invention, which is defined in theclaims.

What is claimed is:

1. The method of fireproofing a cellulose structure which comprisespreparing an aqueous solution of an ammonia complex of a neutral salt ofa heavy metal capable of complexing with ammonia and a partial ester ofphosphoric acid in which 1 to 2 of the active hydrogens of phosphoricacid is replaced by the residue of an alcohol or phenol, said residueswhen alkyl containing an average of 4 to 6 carbon atoms each whenunsubstituted or alkoxy-substituted and at least 3 carbon atoms whenhalo-substituted with chlorine or bromine, and containing no more carbonatoms per residue than indicated by the formula C atoms minus Cl atomsminus 2(Br) atoms=6 for alkyls and C atoms minus Cl atoms minus 2(Br)atoms: 10 for aryls absorbing suflicient solution into the cellulosicstructure to impart flame-retardant properties thereto, and evaporatingthe bulk of the water and sufficient ammonia from the complex toprecipitate the water-insoluble metallicorganic phosphate to produce afire-retardant structure resistant to leaching by Water.

2. The method of claim 1 in which the heavy metal is 5 3. The method ofclaim 1 in which the heavy metal is copper.

4. The method of claim 1 in which the organic residues are substitutedwith chlorine or bromine.

5. The method of claim 1 in which the heavy metal is zinc or copper andthe organic groups are selected from N-butyl, phenyl, chlorinatedpropyl, chlorinated butyl, and brominated propyl.

References Cited UNITED STATES PATENTS 3,650,820 3/1972 DiPictro117--136 WILLIAM D. MARTIN, Primary Examiner J. A. BELL, AssistantExaminer US. Cl. X.R.

106-15 FP; 1l7-137; 2528.1

UNITED STATES PATENT OFFICE I, CERTIFICATE OF CORRECTION Patent No. 3,7l0,26 -l Dated June 19, 1973 Inv nmfl Charles Andrew Lynch, Jr. EdwardFrancis Orwoll It is certified that error appears in theabove-identified patent bed that said Letters Patent'are herebycorrected as shown below:

Column 1, line 31, "nit" should read --not-.

Column 1, line 67, "filame" should read --flame--.

olumn 2, line 3, "0t" should read -to--.

co umn 2, line 31, "alcolol" should read --alcohol.

Column 3, line 38, "in turn less" should read --in turn dipping; less--.I I

Column l, line 63, "cuupric" should. read --'c upric Table 1, Column 5,line 1 4, "specimen" should read .Specimens-. Table 1, Column 5, line2l, "specimen" should read -Specimens. Table 1, Column 5, line 27,"13.5" should read l3.l-

Column 5, line 16, "desecribed" should read --described-.

Column 6, line 73, "aryls" should read -aryls,--.-

Signed and sealed 'this 1st day of January 197E.

(SEAL) Attest:

EDWARD M.FLEICI-IER,JR. RENE D. TEGTMEYER Attesting Officer ActingCommissioner of Patents 11.5. GOVIRNNINT PRINTING OIHCE I90, O-S')34 4UNITED STATES PATENT OFFICE I C CERTIFICATE OF CORRECTION Patent No.3,740,26 Dated June 19, 1973 Inventor-"( Charles Andrew Lynch, Jr. 1Edward Francis Orwoll It is certified that error appears in theabove-identified patent that said Letters Patent are hereby corrected asshown below:

Column 1, line 31, "nit" should read -not-.

Column 1, line 67, "filame" should read -vflame--.

olumn 2, line i 3, "0t" should read to-.

Column 2, line 3i, "alcolol" should read -aloohol-.

Column 3, line 38, "in turn less" should read --in turn dipping;

less. l r

Column l, line 63, "cuupric" should read --oupric-i-. Table 1, Column 5,line l t, "specimen" should read --Specirnens--. Table 1, Column 5, line21, "specimen" should read -Specimens--. Table 1, Column 5, line 27,"13.5" should read 13.1--

Column 5, line H6, "desecribed should read -described-.

Column 6, line 73, "aryls" should read -aryls,-.

Signed and sealed this 1st day of January l97ll.

(SEAL) Attestz' EDWARD M.FLETCHER,JR. RENE D. TEGTMEYER AttestingOfficer Acting Commissioner of Patents F OR 5 0-1050 ii-59} USCOMIM-DC60376-PG9 h 0.5. GOVIINIIINY rann'mc omc: no o-:u-:u

